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Bash stands for Bourne Again Shell. It is a command-line shell and scripting language used mainly in Linux and Unix systems.

Bash allows users to:

• Run commands
• Automate tasks
• Create shell scripts
• Manage files and processes

#!/bin/bash
echo "Hello World"

A shell script is a file containing a sequence of Bash commands that are executed automatically.

Shell scripts help automate repetitive tasks.

#!/bin/bash

name="AK"

echo $name

Variables in Bash are declared without data types.

No spaces should be used around =.

#!/bin/bash

name="AK"

echo $name

Arithmetic operations in Bash are usually done using $(( )).

#!/bin/bash

num1=10
num2=20

sum=$((num1 + num2))

echo $sum

An if statement is used to execute commands conditionally.

#!/bin/bash

if [ 10 -gt 5 ]
then
  echo "10 is greater"
fi

A for loop is used to repeat commands multiple times.

#!/bin/bash

for i in 1 2 3 4 5
do
  echo $i
done

A while loop repeatedly executes commands while a condition remains true.

#!/bin/bash

count=1

while [ $count -le 5 ]
do
  echo $count
  count=$((count + 1))
done

Functions are reusable blocks of code used to perform specific tasks.

#!/bin/bash

function greet() {
  echo "Hello AK"
}

greet

Positional parameters are command-line arguments passed to a script.

• $1 → first argument
• $2 → second argument
• $# → total arguments

#!/bin/bash

echo $1
echo $2

The read command is used to take input from the user.

#!/bin/bash

read -p "Enter your name: " name

echo "Welcome $name"

Bash provides test operators to check files and directories.

#!/bin/bash

touch file.txt

if [ -f file.txt ]
then
  echo "File exists"
fi

A case statement is used for multiple condition checks.

#!/bin/bash

case $1 in
  start)
    echo "Starting"
    ;;
  stop)
    echo "Stopping"
    ;;
  *)
    echo "Invalid option"
    ;;
esac

Arrays store multiple values in a single variable.

#!/bin/bash

arr=("apple" "banana" "mango")

echo ${arr[0]}
echo ${arr[1]}

Command substitution allows the output of a command to be stored in a variable.

#!/bin/bash

today=$(date)

echo $today

grep is a command used to search text patterns inside files.

#!/bin/bash

grep "hello" file.txt

The ps command shows running processes.

#!/bin/bash

ps aux | grep nginx

The find command searches for files and directories.

#!/bin/bash

find . -name "*.txt"

chmod changes file permissions in Linux.

#!/bin/bash

chmod +x script.sh

tar is used to archive and compress files.

#!/bin/bash

tar -czvf backup.tar.gz folder/

Environment variables store system-wide values used by the shell and applications.

#!/bin/bash

#!/bin/bash

echo "Current User: $USER"
echo "Home Directory: $HOME"

Every command in Bash returns an exit status.

• 0 → Success
• Non-zero → Error

#!/bin/bash

echo "Exit Status: $?"